A recent study provides insight into the dynamic interplay between glaciers, climate change and mountain-building. The study, conducted in northern Patagonia, pieces together several types of evidence to develop a picture of mountain formation over past geological periods, and it highlights that glaciers can influence mountain-building processes.
Mountains are formed when giant pieces of the Earth’s crust, known as tectonic plates, collide with one another and thrust trillions of tons of rock (or other material) upward. “The idea of glaciers affecting mountain-building processes has been around for a while, but there has been a lack of study on the specific processes and how exactly it could happen,” said Mike Kaplan, a geologist at the Lamont-Doherty Earth Observatory of Columbia University who was not involved with the recent study. The study focuses on the area just to the east of the North Patagonian Andes, which the authors call the foreland, in an attempt to see a wider scope of the glaciers’ impact — something that past studies have not done.
The North Patagonian Andes lie along the political border between Chile and Argentina. The region contains a vast mountain range, basins, glaciers, lakes and much more. It is believed to have formed between 1 billion and 2.1 billion years ago. While these colossal protrusions in the Earth’s crust have been standing for what seems like forever, they certainly have not been standing completely still.
During the late Miocene Epoch, between 13 and 7 million years ago, the region experienced low levels of glaciation. And during this time, the foreland of the region underwent more uplift along its thrust faults. A thrust fault describes a fracture between two blocks of rock, with one block sliding over the other.
In an interview with GlacierHub, Roger Buck, a geologist at the Lamont-Doherty Earth Observatory, explained that “landscapes can evolve over time to a steady state, but if you change things, that ‘quasi-equilibrium’ is thrown off.”
Between 7 million to 3 million years ago, the Patagonian Andes experienced new, high levels of glaciation and ice cover, thus changing that steady state. The mountain valleys held glaciers that stretched from high peaks down to the lowlands. This new and heavy onset of glaciation that occurred in Patagonia created an imbalance within the landscape’s “quasi-equilibrium,” as the glaciers caused erosion and increased the flow of sediment down the mountains. In other words, the glaciers significantly altered the mountains’ structures. Coinciding directly with the glacial onset was a reduction in the thrust fault activity that occurred before the glaciers appeared.
Exploring some of the specific physical interactions which took place, Kaplan explained the phenomenon of uplift/rebound. “When glaciers erode the surface of the mountain, they are clearing large and heavy masses, thus allowing the mountains to rise up.” However, when the glaciers are present, their immense weight will inhibit uplift as well. Once they have retreated and eroded the surface, uplift can occur again.
Kaplan also highlighted the authors’ hypothesis with regard to the increase in sediment flow. “The authors are postulating that the glaciers carry sediment down into the subduction zones, which further affects the mountain-building processes.” Subduction zones are located where tectonic plates actually meet and pass over and under each other. The Nazca Plate, located under the Pacific Ocean, slides under the South American Plate on the continent’s west coast, creating the Andes. As the glacier-carried sediment flows west and into the ocean, it sinks down and lubricates the interface of the plates, changing how they interact. However, as fault activity in the eastern Patagonian foreland slowed down, the sediment, which used to collect in the basins, began to bypass the land and deposit offshore into the Atlantic, diverted from the subduction zone.
The authors were able to develop this timeline by using earlier research findings and by conducting fieldwork throughout the region, capturing evidence of what the mountains and nearby regions were like millions of years ago. Using uranium-lead and beryllium dating methods, the authors were able to determine where and when specific deformations occurred in the region. They compared the timing of these events to the timing of the glaciation period, and found a significant correlation.
The authors concluded that increased glaciation and erosion affect the mountain-building processes in this region by shifting the distribution of mass and sediment, given that the changes in mountain-building activity coincide directly with the glacial onset approximately 7 million years ago. Furthermore, they concluded that levels of glaciation are directly affected by climate change.
While theoretical analyses and model estimates previously arrived at the same conclusion — that climate change and glaciers affect mountain-building processes — this study provides field observations and hard evidence for this natural phenomenon. Kaplan also emphasized the importance of the study’s area of focus. Most studies in the past have looked at the core of the mountain range, but this study explores an area beyond the heart of the mountains as well, much further from the glaciers themselves.
“I’ve driven along those roads myself and never realized the glaciers’ influence reached so far,” Kaplan said. “The authors’ work should increase appreciation for the role of glaciers and climate change in affecting mountain-building processes and the region surrounding the mountains too.”
With glaciation levels around the world shifting along with an ever-changing climate, mountains may continue to move — a reminder of the dramatic changes that human activity is causing in every part of the Earth.